Variable amplitude vibration generator

ABSTRACT

A variable amplitude vibration generator especially adapted for use with compacting machines in which a primary weight is eccentrically fixed to a power driven rotatably mounted shaft and a secondary weight eccentrically freely rotatably mounted on the shaft is releasably securable to the shaft by activating a remotely controllable detent connection, in an in-phase relationship with the primary weight to provide high amplitude vibration, and in which - upon rotation of the shaft in either direction though slightly less than 180* - with the detent connection deactivated, an out-of-phase relationship is established between the primary and secondary weights to provide for low amplitude vibration.

United States Patent Takata 1 Sept. 30, 1975 [54] VARIABLE AMPLITUDEVIBRATION 3.797.954 3/1974 Harris 404/117 3,814,532 6/1974 Barrett404/117 GENERATOR [75] Inventor: Harry H. Takata, Golden Valley,

Minn.

[73] Assignee: Raygo, Inc., Minneapolis Minn.

[22] Filed: Nov. 7, 1974 [21] Appl. No.: 521,754

[52] US. Cl. 404/117; 404/133 [51] Int. Cl. EOIC 19/38 [58] Field ofSearch 404/117, 133; 74/87 [56] References Cited UNITED STATES PATENTS3,192,839 7/1965 Vivier .Q 404/117 3,598,029 8/1971 Paramythioti.. 404/117 3.605.584 9/1971 Kaltenegger 404/117 3,670,631 6/1972 Gaylord 404/1173.722381 3/1973 Tuneblom 404/1 17 Primary Examiner-Nile C. Byers Jr.

[57] ABSTRACT A variable amplitude vibration generator especiallyadapted for use with compacting machines in which a primary weight iseccentrically fixed to a power driven rotatably mounted shaft and asecondary weight eccentrically freely rotatably mounted on the shaft isreleasably securable to the shaft by activating a remotely controllabledetent connection, in an in-phase relationship with the primary weightto provide high amplitude vibration, and in which upon rotation of theshaft in either direction though slightly less than 180 with the detentconnection deactivated, an out-ofphase relationship is establishedbetween the primary and secondary weights to provide for low amplitudevibration.

21 Claims, 12 Drawing Figures US. Patent Sept. 30,1975 Sheet 1 of73,909,147

PIC-Q US. Patent Sept. 30,1975 Sheet 2 of7 3,909,147

U.S. Patsnt Sept 30,1975 Sheet 3 of7 $909,147

US. Patent Sept. 36,1975 Sheet 4 of7 3,909,147

US. Patent Sept. 30,1975 Sheet 7 of7 3,909,147

F'IGJO.

MEDIUM AMPLITUDE 29 154 2W ag/mg I VARIABLE AMPLITUDE VIBRATIONGENERATOR This invention relates to vibration generators and refers moreparticularly to variable amplitude vibration generators especiallyadapted for use in compacting and surface finishing machines. Suchmachines, equipped with variable amplitude vibration generators of oneform or another, have been available heretofore. The Barrett et al. U.S.Pat. No. 3,814,532 and the Tuneblom US. Pat. No. 3,722,381 illustrateexamples of such prior vibration generators. Like the variable amplitudegenerators of these patents, the vibration generator of this inventionemploys primary and secondary weights eccentrically mounted on a powerdriven shaft, the primary weight being fixed to that shaft and thesecondary weight being movable with respect to the shaft between a highamplitude position and a low amplitude position.

The machines of the aforesaid two patents are capable of reasonably goodperformance, but they leave room for improvement. To illustrate, whilethe vibration generator of the Tuneblom patent has the advantage ofsimplicity and few parts as a result of its capability of being switchedfrom low to high amplitude vibration generation and vice versa by simplychanging the direction of rotation of the power driven shaft on whichits eccentric weights are mounted, the need for changing the directionof that rotation constitutes a serious disadvantage. It has been knownfor quite some time as evidenced by the German Pat. No. 1,255,591, whichhas a 1957 filing date that unless the direction of rotation of theeccentric weights is correlated with the direction the machine istravelling, the quality of the sur' face being compacted suffers. Thereason for this as explained in the aforesaid German patent and also inUS Pat. No. 3,605,583 lies in the fact that rotation of the eccentricmass in the same direction the drum turns during traverse of the machinepromotes uniformity in compaction of the surface being worked,especially an asphalt surface, whereas rotation of the eccentric mass inthe direction opposite that of the drum results in skipping and bumpingof the drum and increases the tractive effort necessary for machinepropulsion.

Thus if the objectionable consequences of not having the direction ofrotation of the eccentric weights at all tage of the Tuneblom machine,and is capable of producing vibration in either the high or lowamplitude mode regardless of the direction in which the machine istraveling so that the direction of rotation of the eccentric weights canbe properly correlated with that of the drum, the hydraulic systememployed in the Barrett et al. machine to effect a shift from oneamplitude mode to the other introduces a significant elementof cost. v

The present invention combines the simplicity of the Tuneblom vibrationgenerator with the versatility of the Barrett et al. machine and does sowith a simple, reliable and inexpensive structure. Accordingly, theinvention achieves a significant improvement in variable vibrationgenerators.

As distinguished from the machine of the Tuneblom patent whichundoubtedly is the most pertinent bit of prior art requiringconsideration in evaluating the patentability of this invention thepresent invention enables the operator to at all times correlate thedirection of rotation of the eccentric weights with the selecteddirection of travel, without constraining his choice between high andlow amplitude vibration, since that choice does not necessitate changingthe direction in which the eccentric weights revolve.

This advantage stems from the fact that when the vibration generator isnot in operation, its eccentric weights automatically assume an in-phaserelationship and that during initial rotation, in either direction, ofthe shaft on which the eccentric weights are mounted, relative motionautomatically takes place between them from that in-phase relationshipto an out-of-phase relationship which places the vibration generator ina low amplitude mode of the same magnitude regardless of the directionof rotation unless a simple mechanical operator-controlled lockingdevice secures the secondary eccentric weights against such rotationrelative to the shaft. This gives the operator a wide latitude of choicein the operation of the machine.

Another important feature of the invention resides in the .manner inwhich the movable secondary eccentric weights are locked or securedagainst displacement from a position in phase with the primary eccentricweights that are fixed to the shaft. This is done by acti vating adetent connected between the hubs of the movable secondary weights andthe shaft while the shaft is stationary and the eccentric weights are intheir in-phase relationship which they automatically assume when theshaft stops turning, the activation of the detent being effected bysimplyshifting an actuator rod that is slidably received in an axialbore in the shaft.

Although the primary objective of the invention is the provision of animproved variable amplitude vibration generator by which either high orlow amplitude vibration can be selectively produced with the eccentricweights rotating in either direction, it is also an object of theinvention to provide a variable amplitude vibration generator capable ofproducing vibration in more than two modes and to accomplish this resultwith a simple, uncomplicated, rugged structure.

With the above and other objectives in mind, the manner in which theinvention achieves its purpose will be appreciated from the followingdescription and the accompanying drawings, which exemplify the invention, it being understood that-changes may be made in the specificapparatus disclosed herein without departing from the essentials of theinvention set forth in the appended claims. 1

The accompanying drawings illustrate several complete examples of theembodiments of the invention constructed according to the best modes sofar devised for the practical application of theprinciples thereof, andin which:

FIG. 1 is a front perspective view of a compacting machine equipped withone form of the variable amplitude vibration generator of thisinvention, attention being directed to the fact that there are actuallytwo duplicate units to the generator both located within the surfacerolling drum of the machine and that the drum is not driven;

FIG. 2 is a longitudinal sectional view through one of the units of thevariable vibration generator embodied in the machine shown in FIG. 1',

FIG. 3 is a cross sectional view through FIG. 2 on the plane of the line3-3, with the primary and secondary eccentric weights in their in-phaserelationship;

FIG. 4 is a view similar to FIG. 3 but showing the eccentric weights intheir out-of-phase relationship;

FIG. 5 is a longitudinal sectional view similar to FIG. 2, butillustrating the vibration generator embodied in a power driven drum;

FIG. 6 is a cross sectional view through FIG. 5 on the plane of the line6--6;

FIG. 7 is a side view of a power driven drum with portions broken awayand in section to especially illustrate the manner in which the drum andthe shaft of the vibration generator are driven;

FIGS. 8 through 11 are a series of longitudinal sectional views througha variable amplitude vibration generator suitable for incorporation inthe drum of a compacting machine, that is capable of operation in fourdifferent amplitude modes, each of said views showing the vibrationgenerator in a different amplitude mode; and

FIG. 12 is a detail sectional view of a portion of the structureillustrated in FIGS. 8-11.

Referring now particularly to the accompanying drawings, and especiallyto FIGS. 1 through 4, the numeral 4 designates the chassis of aself-propelled surface compacting machine of the type employed in thepaving of streets and roadways. The machine illustrated in FIG. I has afreely rotatable i.e. not power driven compacting drum 5 at its frontend and a pair of power driven traction wheels 6 at its rear. As iscustomary, power is delivered to the traction wheels 6 from the powerplant of the machine (not visible in FIG. 1) under control of anoperator who occupies a seat 7 that is located behind a steering wheel 8by which the operator steers the machine. For that purpose, the drum assembly and the chassis of the machine are articulately connected forrelative rotation about an upright axis. Details of the steeringmechanism and of the reversible propulsion system through which power isdelivered to the rear traction wheels being conventional and well knownare not shown.

As is conventional, the drum assembly comprises a rigid yoke, the arms 9of which embrace the drum and have bearing mounting plates 10 connectedthereto by elastic shock mounts 11 (see FIG. 2). The bearing plates 10are adjacent to the ends of the drum and have fixed thereto acylindrical housing 12 in which the outer races of bearings 13 aremounted. The inner races of the bearings 13 are seated on the hubs 14 ofthe drum. In this manner the drum is freely rotatably connected with themounting plates and, through the shock mounts 11, with the arms 9 of theyoke. Vibration of the drum is therefore not imparted to the rest of themachine. Although FIG. 2 shows only the aforesaid structure at one endof the drum, it is to be under stood that this same structure isduplicated at the other end of the drum. With that understanding, thefollowing description will concern itself only with the structure at oneend of the drum.

The drum 5 is hollow, as is customary, and each of its opposite endwalls 15 has a cup-shaped housing 16 welded thereto. This housing isconcentric with the drum and has a flange 17 that encircles the hub 14of the drum bolted thereto. The inner end wall 18 of the housing 16 andthe flange 17 that encircles the hub 14 have bearings 19 mountedtherein. These bearings are coaxial and rotatably mount a tubular shaft20 that extends for the full length of the drum and is coaxialtherewith.

Mounted on the shaft 20 inside each housing 16 is one of the two units,designated generally by the numeral 21, of the variable vibrationgenerator of this invention. The two units are identical. Each comprisesa primary weight 22 that is eccentrically fixed to the shaft 20 as bybeing welded thereto and a secondary weight 23 freely eccentricallyrotatably mounted on the shaft but securable thereto by a manuallycontrollable detent type locking device to be described later. Theprimary weight consists of a pair of generally bellshaped plates 25fixed to the opposite sides of an arcuate spacer block 26. One of theplates is welded to the spacer block and the other is secured thereto bycap screws 27. As shown in FIGS. 3 and 4, the spacer block 26 conformsin shape and size to the wide bottom edge portions of the bell shapedside plates. Preferably the arcuate spacer block and the bottom edge ofthe side plates are concentric with the shaft 20.

The upper stem portions 28 of the side plates which can be considered asarms that extend radially from the shaft 20 are connected by a cross bar29, one end of which is welded to the side plate that is welded to theshaft. The other end of the cross bar is fixed to the adjacent sideplate by a cap screw 30.

The secondary weight 23 is journalled on the shaft between the two sideplates 25 and has its center of gravity spaced radially a substantialdistance from the axis of the shaft so that the secondary weight hangsfrom the shaft in the position shown in FIG. 3 when the shaft is notturning. In fact, the primary weight also assumes the pendent positionshown inFIG. 3 when the shaft is not turning. In that condition, the twoeccentric weights occupy an in-phase relationship.

However, during initial rotation of the shaft in either direction, theprimary weight moves away from its position in phase with the secondaryweight and, after slightly less than of rotation of the shaft, the crossbar 29 collides with a lug 31 that projects from the arcuate edge 32 ofthe secondary weight and constitutes its radially outermost portion.Upon such collision, the eccentric weights are almost completely inout-ofphase relationship, as shown in FIG. 4. As long as the shaftcontinues to turn in the direction that brought about the collision ofthe cross bar 29 with the lug 31, the weights remain in theirout-of-phase relationship. Since the secondary weight is lighter thanthe primary weight, it only partially counterbalances the primaryweight, so that with the weights thus disposed the vibration generatoris in its low amplitude mode.

Since, as shown in FIG. 3, the cross bar 29 and the lug 32 aresymmetrically disposed with respect to a vertical plane coincident withthe axis of the shaft, the angle through which the aforesaid relativerotation between the secondary weight and the shaft extends in effectingthe described out-of-phase relationship is the same regardless of thedirection of rotation. Hence the magnitude of the low amplitudevibration is the same for either direction of rotation.

The high amplitude mode is obtained by locking the secondary eccentricweight against rotation about the shaft from its position in phase withthe primary weight, which position it automatically assumes when theshaft stops rotating. This is done by the previously mentioneddetent-type locking device. As best shown in FIGS. 3 and 4, this lockingdevice comprises a pair of coaxial detents or sockets 32 indiametrically opposite portions of the hub 33 of the secondary weightand a pair of locking balls 34 in the outer end portions of a cross bore35 extending diametrically through the shaft. Both the detents and thecross bore are equispaced from the side plates 25 of the primaryeccentric weight. Hence, the detents and the cross bore can be broughtinto alignment enabling the locking balls to be projected into thedetents to secure the secondary weight to the shaft. That alignmentobtains when the shaft is not turning and both weights are in thependent position, as shown in FIG. 3. Absolute freedom for the secondaryweight to assume a pendent position is assured by providing its hub withsuitable anti-friction bearings 33 that are spaced apart to, in effect,form a circular groove 38 in the hub.

To enable assembly of the locking device, the detents or sockets 32 arein the inner ends of a pair of studs 36 threaded into coaxial tappedholes in the hub 33 and secured against displacement by lock nuts 37.

Preferably the cross bore 35 has its end portions lined by sleeves 39that provide runways for the balls 34 and facilitate in and out movementof the balls.

The balls 34 are cammed out of the ends of the cross bore 35 and intothe detents or sockets 32 by a conically shaped shoulder 40 on a rod 41that is slidably re ceived in a bore 42 extending axially through theshaft 20. The shoulder 40 is formed by the step in the diameter of therod. With the rod in a position at which its small diameter portion isaligned with the cross bore 35 in the shaft, the balls 34 are free toleave the detents or sockets 33 and roll around the circular annulargroove 38 in the hub 32, but when the rod is shifted to bring its largediameter portion into alignment with the cross bore, the balls 34 areforced into locking engagement with the detents or sockets 32.

To avoid objectionably large dimensions for the locking balls and thecross bore, spacer balls 43 are interposed between the balls 34 and therod 41.

Any suitable actuating means can be employed to shift the rod 41 to andfrom its position securing the eccentric weights in their in-phaserelationship. For illustrative purposes, in FIG. 2 a fluid pressurecylinder 44 is mounted in fixed relation with the mounting plate 1 1.This cylinder is coaxial with the drum and its piston 45 is connectedwith the rod 41 through a rotation accommodating coupling 46. Fluidpressure delivered to the cylinder through a supply line 47 projects thepiston 45 and the rod to the left (in FIG. 3) to cam the balls 34 intolocking engagement with the detents or sockets 32. Retraction of thepiston and the rod upon reduction of pressure in the cylinder iseffected by a spring 48 reacting between the piston and the inner end ofthe cylinder.

As in the machine of the Barrett et al. US. Pat. No. 3,814,532, the twounits of the variable amplitude vibration generator are mounted uponseparate coaxial shafts connected by a torque tube to which they arejoined by flexible couplings A reversible hydraulic motor mounted on theplate 10 at one-end of the drum,

is drivingly connected to the adjacent shaft 20 through a conventionalflexible coupling. This motor is not shown in FIG. 2 but is indicated indotted lines in FIG. 1 and also shown in FIGS. 5 and 7, in each of whichit is identified by the numeral 50. FIGS. 5 and 7 also identify by thenumeral 50' the flexible coupling through which driving torque istransmitted to the connected shafts 20 from the motor. Energization ofthe motor 50 as well as its direction of rotation is controllable in thecustomary manner by the operator of the machine, and as is alsoexplained in the Barrett et al. patent selection of the direction ofrotation of the motor is preferably automatically coordinated with theselection of the direction of traverse of the machine, so that thehorizontal components of force resulting from operation of the vibrationgenerator will not oppose propulsion of the machine.

In the embodiment of the invention just described and shown in FIGS. 14,the drum is not driven so that it does not contribute to the propulsionof the machine by the traction wheels 6. Obviously, of course, thevariable amplitude vibration generator of this invention is alsoadaptable to a compacting machine in which the drum is driven. FIGS. 5-7illustrate this adaptation of the invention. It differs from thestructure just described only in the manner in which the control rod 41is shifted and that difference is entailed by the fact that access tothe outer ends of both shafts 20 is obstructed at one end by thehydraulic motor 50 and at the other end by a hydraulic motor 51 thatdrives the drum.

FIG. 7 illustrates the positional relationship between the two motorsand the outer ends of the shafts 20.

The rod shifting mechanism in this embodiment of the invention comprisesa fork 52 pivoted to swing about a fixed axis established by bearings 53that are mounted in the wall of a cylindrical housing 54 that isconnected to the adjacent bearing plate that is connected through shockmounts with the adjacent arm of the yoke 9, none of which structureappears in FIGS. 5 and 6. The cylindrical housing 54 corresponds to thehousing 12 of the previously described structure (see FIG. 2) and hasthe outer race of one of the drum bearings 13 mounted therein.

The arms of the fork 52 are fixed to a tube 55 (see FIG. 6) which inturn is fixed to a shaft 56 that is journalled in the bearings 53 andhas a lever 57 secured to one end thereof. That lever is connected tothe plunger 58 of an air cylinder 59 pivotally anchored to a bracket 60that is bolted to the housing 54. Hence, by controlled introduction ofair pressure into the opposite ends of the cylinder59, the shaft 56 canbe oscillated to rock the fork 52 from one position to the other of itsrange of motion defined by stops 61 and 62 that are mounted on thebracket 60.

The extremities of the arms of the fork 52 are bifurcated to receivetrunnions 63 that project coaxially from a ring 64 formed of two halfsections bolted together. This ring encircles a sleeve 65 that isslidably and freely rotatably mounted on the adjacent end portion 66 ofthe shaft 20. The ring 64 has a groove opening to its inner surface toreceive a flange 67 on the sleeve and thereby freely rotatably connectthe ring with the sleeve. Accordingly, upon rocking motion beingimparted to the fork, the sleeve is shifted axially along the endportion 66 of the shaft 20. That axial motion of the sleeve is impartedto the rod 41 through a bolt 68 that passes through a cross bore in theadjacent end portion of the rod and slides in longitudinal slots 69 inthe shaft portion 66, it being understood that the shaft 20 is tubularfrom end to end to accommodate the rod 41. By virtue of the bolt 68being received in the slots 69, the rod 41, the shaft 20 and the sleeve65 rotate in unison, such rotation being imparted thereto in theselected direction by the motor 50 which is drivingly connected to theshaft.

As will be readily apparent, with the actuating mechanism justdescribed, the rod 41 can be shifted from its low amplitude position toits high amplitude position, despite the fact that the motor 50obstructs access to the adjacent end of the rod.

To the extent that the structure shown in FIG. has not been described,it comports with that shown in FIG. 2, and accordingly is identified bythe same reference numerals.

The two embodiments of the invention that have been described providefor only a low and a high amplitude of vibration, whereas in thatembodiment of the invention shown in FIGS. 8-12, vibration at any offour different levels of amplitude can be had. In this fourmode system,there is a single primary eccentric weight 70 and two secondaryeccentric weights a heavy one 71 and a light one 72. To accommodate thetwo secondary weights, the side plates 25' of the primary weight arefarther apart than they are in the previously described two-modevibration generator, and accordingly the crossbar 29 is longer, so thatthe crossbar will collide with either or both of the secondary weightsduring initial rotation of the drive shaft 20, depending upon which ofthe secondary weights is free to turn about the shaft.

The secondary weights are individually and selectively securable to theshaft by ball detent locking devices that are identical with that of thedescribed twomode system, but for each unit of the vibration generatorthe rod 41' has two small diameter portions and four conical shoulders40 formed by the steps between the small and large diameter portions ofthe shaft. These shoulders are so located with respect to each other andthe hubs of the two secondary weights that in each of four differentaxial positions of the rod, a different amplitude of vibration isobtained. Thus, as indicated in FIG. 8, low amplitude vibration resultswhen the heavier of the two secondary weights is free to assume anout-of-phase relationship with the primary weight and the lightersecondary weight is locked in its in-phase relationship with respect tothe primary weight.

Minimum amplitude vibration results from having both secondary weightsfree to assume out-of-phase relationship with the primary weight, asillustrated in FIG. 9; medium amplitude vibration is obtained when onlythe lighter one of the two secondary weights is free to assume itsout-of-phase relationship with the primary weight, as shown in FIG. 10;and high amplitude vibration is obtained when both secondary weights arelocked to the shaft, as in FIG. 11.

While any suitable means may be employed to shift the rod 41 to itsdifferent positions shown in FIGS. 8-11, a multiple-position fluidpressure cylinder 80 has been found to be entirely satisfactory.Cylinders of this type are commercially available and, since it forms nopart of the present invention, a detailed description thereof is notneeded. Suffice it to say that the cylinder has four ports, designatedA, B, C, and D, through which fluid pressure is introduced toselectively effect movement of the piston in the cylinder to each offour different positions, in each of which it holds the rod 41 in theposition establishing the selected amplitude mode. The arrows oppositethe different ports identify which of them that are connected with thesource of fluid pressure to place the vibration generator in theamplitude mode shown in each of the four views of the series.

Inasmuch as the rod 41 rotates with the shaft 20, a rotationaccommodating coupling 81 connects the rod with the rod 82 of the pistonin the cylinder 80. FIG. 12 illustrates the construction of the coupling81. As there shown, the coupling comprises a cup-shaped body that isconnected to the rod 41 by a clevis 84 and contains a ball bearing 85.The outer race of the bearing is secured in the cup-shaped body and itsinner race is secured to the piston rod 82.

As in the first described embodiment of the invention, in thisfour-amplitude version, the shaft 20 of the vibration generator isdriven by a hydraulic motor at the end of the drum remote from that atwhich the shifting mechanism for the rod 41' is located.

Although the operation of the variable amplitude vibration generator ofthis invention is no doubt readily understandable from the foregoingdescription, a brief recapitulation may be welcome. With the machinestationary and the shaft on which the eccentric weights are mounted notturning, the weights are in their inphase pendent positions (FIG. 3).For low amplitude vibration, the secondary lighter weights must be freeto turn with respect to the shaft. That assured, upon initial rotationof the shaft, the primary eccentric weights rotating therewith will bemoved from in-phase towards out-of-phase relationship with the secondaryeccentric weights. After somewhat less than of rotation, the primaryweights collide with the secondary weights and then they move in unison.This takes place automatically whether the shaft rotates clockwise orcounterclockwise, and as long as the shaft continues to rotate in theselected direction, the primary and secondary weights remain in theirout-of-phase partially counterbalancing relationship and produce lowamplitude vibration of the same magnitude regardless of the direction ofrotation.

If high amplitude vibration is selected, the secondary weights aresimply secured against rotation about the shaft in their in-phaserelationship with the primary weights, that securement being effected byactivating the ball detents.

Those skilled in the art will appreciate that the invention can beembodied in forms other than as herein disclosed for purposes ofillustration.

The invention is defined by the following claims:

I claim:

1. A variable amplitude vibration generator comprising:

A. a rotatably mounted shaft;

B, a primary weight eccentrically fixed to the shaft to rotatetherewith;

C. a lighter secondary weight;

D. means freely rotatably mounting the secondary weight eccentrically onthe shaft, said weights occupying pendent in-phase positions when theshaft is not turning;

E. power means to impart rotation to the shaft in either direction;

the freedom for relative rotation between the secondary weight and-theshaft enabling the secondary weight to remain in its pendent positionwhile the shaft begins to turn and moves the primary weight out of phasewith the secondary weight; and y F. means to limit relative rotation ineitherdirection between the shaft and the secondary weight tosubstantially less than 360, so that upon-rotation of the shaft ineither selected direction, the two weights become connectedin anout-of-phase partially counter-balancing relationship placing thevibration generator in a low amplitude mode of substantially the samemagnitude regardless of the direction of rotation which mode it retainsas long as .the shaft continues to turn in said selected direction. v

' 2. The variable amplitude vibration generator of claim I whereinrelative rotation in either direction betweenthe shaft and the secondaryweight is limited to a few degrees less than 180 so that in each casesaid out-of-fphase relationship is slightlylessthan complete.

3. The variable amplitude vibration generator of claim 1', furthercharacterized by detent meansfor 're'leasably securingthe secondaryweight against rotation relative to the shaft in a pos'ition' in whichit is in phase with. the primary weight, so that upon rotation of theshaft while the secondary weight is thus secured thereto the vibrationgenerator operates in a high amplitude mode. .4. The, variable amplitudevibration generator of claim 1, wherein f the center of gravity' of theprimary weight and the means to limit relative rotation between theshaft and the secondary weight are at opposite sides of the shaft andwherein said means tolimit relative rotation between the shaft and thesecondary weight comprises: i i 1. an arm fixed with respect toandprojecting radially from the shaft; and. 2. an abutment on said armin position with a surface on the secondary weight that spacedfrom theaxis of the shaft. 5. The variable amplitude vibration claim 4 whereinsaid surface with which said'abutment generator of to collide collidesis on a lug that projects from the radially outermost portion of thesecondaryweight. 6. The variable amplitude vibration 8. The variableamplitude vibration generator of claim 3, wherein the secondary weighthas a hub in the bore of which the shaft is freely rotatably received,

and wherein said detent means comprises:

1. socket means in said hub and in the shaft which align with oneanother when the two weights are in phase;

2. a locking member movably received in the socket means in the shaftfor movement between a retracted position disengaged from the socketmeans in said hub and a projected position engaging both socket means;and

3. actuating means longitudinally shiftably carried by the shaft to movesaid locking member to and hold it in its projected position.

9. The variable amplitude vibration generator of claim 8, wherein thesocket means in said hub comprises diametrically opposite socketsopening to the bore of the hub,

wherein the socket means in the shaft comprises a cross bore extendingdiametrically through the shaft,

and wherein said locking member comprises a ball in each end portion ofsaid cross bore.

10. The variable amplitude vibration generator of claim 9, wherein saidactuating means comprises a round rod slidable'in anaxial bore in theshaft that intersects said cross bore, said rod having large and smalldiameterportions either of which can be brought into alignment with thecross bore by axially shifting the rod, so that in one axial position ofthe rod with respect to the shaft, said balls are free to leaveengagement with the sockets in said hub, while in another axial positionof the rod the balls are held seated in said sockets in the hub.

11. The variable amplitude vibration generator of claim 10, furthercharacterized by a means for imparting axial movement to saidrod withrespect to the shaft.

'12. The variable amplitude vibration generator of claim 11, wherein. atleast one of the steps between the large andsmall diameter portions ofthe shaft is conical, so that during axial movement of the rod in thedi- I rection to align its large diameter portion with which saidconical step connects, with the cross bore, said step serves as a cam toeffect projection of the balls into member with spaced arms that have afixed connection with the shaft and that project radially from the shaftin the same direction, i I

and wherein the secondary weight is located between said arms.

7. The variable amplitude vibration generator of claim 6, wherein themeans to limit relative motion between the shaft and the secondaryweight comprises:

i 1. an extension on each of said spaced arms projecting radially fromthe shaft in the direction opposite that in which said spaced armsproject from the shaft;

2. a crossbar connecting the outer end portions of said extensions; and

3. a lug on the secondary weight spaced from the axis of the shaft adistance to have said crossbar collide therewith upon rotation of theshaft in either direction.

said sockets in the'hub'.

13. The variable. amplitude vibration generator of claim-12, whereinasecond pair of balls is located in said cross bore,'one between each ofthe first named balls and the rod. I

, 14. The variable amplitude vibration. generator of claim 11, whereinthe means for imparting endwise movement to the rod comprises a fluidpressure cylinder fixed against movement axially of the'shaft, and apiston in the cylinder connected with the rod to impart movement theretoupon connection of the cylinder with a source of fluid pressure.

15. The invention defined by claim 11, further characterized in that thevariable amplitude vibration generator is associated with a compactingmachine having a frame and a drum rotatably and supportingly connectedwith the frame, with the shaft of the vibration generator coaxial withand inside the drum,

wherein said means for imparting axial movement to the rod is carried bythe frame of the machine at one end of the drum, and wherein said powermeans to impart rotation to said shaft is carried by the frame of themachine at the other end of the drum.

16. The variable amplitude vibration generator of claim 11,

wherein the variable amplitude vibration generator is associated with acompacting machine having a frame and a drum rotatably and supportinglyconnected with the frame, with the shaft of the vibration generatorcoaxial with and inside the drum, wherein a motor carried by the frameof the machine at one end of the drum is drivingly connected with thedrum to impart rotation to the drum, wherein a motor carried by theframe of the machine at the other end of the drum is coupled to theshaft of the vibration generator to impart rotation to it, and whereinsaid means for imparting axial movement to the rod is carried by theframe of the machine at said last named end of the drum, and so locatedthat it does not interfere with the driving connection between the shaftof the vibration generab r and its motor.

17. The variable amplitude vibration generator of claim 3, wherein thereare a plurality of secondary weights eccentrically freely rotatablymounted on the shaft, and separate detent means for each secondaryweight, so that by selective actuation of said separate detent means,the vibration generator can be set to produce vibration at more than twodifferent amplitudes.

18. The variable amplitude vibration generator of claim 17, wherein thesecondary weights differ in weight.

19. The variable amplitude vibration generator of claim 17, whereinthere is but one primary weight that is heavier than any of thesecondary weights.

20. The variable amplitude vibration generator of claim 19, wherein A.there are two secondary weights each of which is eccentrically'mounted nthe shaft by a hub in the bore of which the shaft is freely rotatablyreceived, and detent means for releasably securing said hub againstrotation relative to the shaft;

B. wherein said detent means comprisesv l. a socket opening to the boreof said hub,

2. a radial bore in the shaft opening to the surface thereof that iswithin the hub to align with the socket in the hub, and

3. a movable element in said radial bore movable between an operativeposition projecting into the socket and an inoperative position free ofthe socket in the hub, the shaft having an axial bore which communicateswith said radial bore;

C. a rod axially slidable in said axial bore, said rod having a smalldiameter portion flanked by large diameter portions for each of said twosecondary weights, alignment of a small diameter portion of the rod.with a radial bore enabling said movable element therein to move to itsinoperative position, and alignment of a large diameter portion of therod with said radial bore holding said movable element in its operativeposition, said small diameter portions of the rod being so spaced withrespect to one another and the two secondary weights, and being of suchlength that l. in one axial position of the rod the hubs of both of saidsecondary weights are secured to the shaft,

2. in a second position of the actuating rod neither of the hubs of thesecondary weights is secured to the shaft,

3. ina third position of the rod only the hub of the heavier of the twosecondary weights is secured to the shaft, and

4. in a fourth position of the rod only the hub of the lighter one ofthe two secondary weights is secured tothe shaft; and

D. means for selectively moving the rod to any one of said fourpositions. v

21. The variable amplitude vibration generator of claim 20, wherein saidradial bore of each of the detent means is a cross bore extendingthrough the shaft,

wherein the hub of each secondary weight has two diametrically oppositesockets opening to its bore, and.

wherein each detent means has two balls, one in each end portion of itscross bore.

1. A variable amplitude vibration generator comprising: A. a rotatablymounted shaft; B. a primary weight eccentrically fixed to the shaft torotate therewith; C. a lighter secondary weight; D. means freelyrotatably mounting the secondary weight eccentrically on the shaft, saidweights occupying pendent inphase positions when the shaft is notturning; E. power means to impart rotation to the shaft in eitherdirection; the freedom for relative rotation between the secondaryweight and the shaft enabling the secondary weight to remain in itspendent position while the shaft begins to turn and moves the primaryweight out of phase with the secondary weight; and F. means to limitrelative rotation in either direction between the shaft and thesecondary weight to substantially less than 360*, so that upon rotationof the shaft in either selected direction, the two weights becomeconnected in an out-of-phase partially counterbalancing relationshipplacing the vibration generator in a low amplitude mode of substantiallythe same magnitude regardless of the direction of rotation which mode itretains as long as the shaft continues to turn in said selecteddirection.
 2. The variable amplitude vibration generator of claim 1,wherein relative rotation in either direction between the shaft and thesecondary weight is limited to a few degrees less than 180 so that ineach case said out-of-phase relationship is slightly less than complete.2. an abutment on said arm in position to collide with a surface on thesecondary weight that is spaced from the axis of the shaft.
 2. acrossbar connectinG the outer end portions of said extensions; and
 2. ina second position of the actuating rod neither of the hubs of thesecondary weights is secured to the shaft,
 2. a radial bore in the shaftopening to the surface thereof that is within the hub to align with thesocket in the hub, and
 2. a locking member movably received in thesocket means in the shaft for movement between a retracted positiondisengaged from the socket means in said hub and a projected positionengaging both socket means; and
 3. actuating means longitudinallyshiftably carried by the shaft to move said locking member to and holdit in its projected position.
 3. a movable element in said radial boremovable between an operative position projecting into the socket and aninoperative position free of the socket in the hub, the shaft having anaxial bore which communicates with said radial bore; C. a rod axiallyslidable in said axial bore, said rod having a small diameter portionflanked by large diameter portions for each of said two secondaryweights, alignment of a small diameter portion of the rod with a radialbore enabling said movable element therein to move to its inoperativeposition, and alignment of a large diameter portion of the rod with saidradial bore holding said movable element in its operative position, saidsmall diameter portions of the rod being so spaced with respect to oneanother and the two secondary weights, and being of such length that 3.in a third position of the rod only the hub of the heavier of the twosecondary weights is secured to the shaft, and
 3. The variable amplitudevibration generator of claim 1, further characterized by detent meansfor releasably securing the secondary weight against rotation relativeto the shaft in a position in which it is in phase with the primaryweight, so that upon rotation of the shaft while the secondary weight isthus secured thereto the vibration generator operates in a highamplitude mode.
 3. a lug on the secondary weight spaced from the axis ofthe shaft a distance to have said crossbar collide therewith uponrotation of the shaft in either direction.
 4. The variable amplitudevibration generator of claim 1, wherein the center of gravity of theprimary weight and the means to limit relative rotation between theshaft and the secondary weight are at opposite sides of the shaft andwherein said means to limit relative rotation between the shaft and thesecondary weight comprises:
 4. in a fourth position of the rod only thehub of the lighter one of the two secondary weights is secured to theshaft; and D. means for selectively moving the rod to any one of saidfour positions.
 5. The variable amplitude vibration generator of claim 4wherein said surface with which said abutment collides is on a lug thatprojects from the radially outermost portion of the secondary weight. 6.The variable amplitude vibration generator of claim 1, wherein theprimary weight is a U-shaped member with spaced arms that have a fixedconnection with the shaft and that project radially from the shaft inthe same direction, and wherein the secondary weight is located betweensaid arms.
 7. The variable amplitude vibration generator of claim 6,wherein the means to limit relative motion between the shaft and thesecondary weight comprises:
 8. The variable amplitude vibrationgenerator of claim 3, wherein the secondary weight has a hub in the boreof which the shaft is freely rotatably received, and wherein said detentmeans comprises:
 9. The variable amplitude vibration generator of claim8, wherein the socket means in said hub comprises diametrically oppositesockets opening to the bore of the hub, wherein the socket means in theshaft comprises a cross bore extending diametrically through the shaft,and wherein said locking member comprises a ball in each end portion ofsaid cross bore.
 10. The variable amplitude vibration generator of claim9, wherein said actuating means comprises a round rod slidable in anaxial bore in the shaft that intersects said cross bore, said rod havinglarge and small diameter portions either of which can be brought intoalignment with the cross bore by axially shifting the rod, so that inone axial position of the rod with respect to the shaft, said balls arefree to leave engagement with the sockets in said hub, while in anotheraxial position of the rod the balls are held seated in said sockets inthe hub.
 11. The variable amplitude vibration generator of claim 10,further characterized by means for imparting axial movement to said rodwith respect to the shaft.
 12. The variable amplitude vibrationgenerator of claim 11, wherein at least one of the steps between thelarge and small diameter portions of the shaft is conical, so thatduring axial movement of the rod in the direction to align its largediameter portion with which said conical step connects, with the crossbore, said step serves as a cam to effect projection of the balls intosaid sockets in the hub.
 13. The variable amplitude vibration generatorof claim 12, wherein a second pair of balls is located in said crossbore, one between each of the first named balls and the rod.
 14. Thevariable amplitude vibration generator of claim 11, wherein the meansfor imparting endwise movement to the rod comprises a fluid pressurecylinder fixed against movement axially of the shaft, and a piston inthe cylinder connected with the rod to impart movement thereto uponconnection of the cylinder with a source of fluid pressure.
 15. Theinvention defined by claim 11, further characterized in that thevariable amplitude vibration generator is associated with a compactingmachine having a frame and a drum rotatably and supportingly connectedwith the frame, with the shaft of the vibration generator coaxial withand inside the drum, wherein said means for imparting axial movement tothe rod is carried by the frame of the machine at one end of the drum,and wherein said power means to impart rotation to said shaft is carriedby the frame of the machine at the other end of the drum.
 16. Thevariable amplitude vibration generator of claim 11, wherein the variableamplitude vibration generator is associated with a compacting machinehaving a frame and a drum rotatably and supportingly connected with theframe, with the shaft of the vibration generator coaxial with and insidethe drum, wherein a motor carried by the frame of the machine at one endof the drum is drivingly connected with the drum to impart rotation tothe drum, wherein a motor carrieD by the frame of the machine at theother end of the drum is coupled to the shaft of the vibration generatorto impart rotation to it, and wherein said means for imparting axialmovement to the rod is carried by the frame of the machine at said lastnamed end of the drum, and so located that it does not interfere withthe driving connection between the shaft of the vibration generator andits motor.
 17. The variable amplitude vibration generator of claim 3,wherein there are a plurality of secondary weights eccentrically freelyrotatably mounted on the shaft, and separate detent means for eachsecondary weight, so that by selective actuation of said separate detentmeans, the vibration generator can be set to produce vibration at morethan two different amplitudes.
 18. The variable amplitude vibrationgenerator of claim 17, wherein the secondary weights differ in weight.19. The variable amplitude vibration generator of claim 17, whereinthere is but one primary weight that is heavier than any of thesecondary weights.
 20. The variable amplitude vibration generator ofclaim 19, wherein A. there are two secondary weights each of which iseccentrically mounted on the shaft by a hub in the bore of which theshaft is freely rotatably received, and detent means for releasablysecuring said hub against rotation relative to the shaft; B. whereinsaid detent means comprises
 21. The variable amplitude vibrationgenerator of claim 20, wherein said radial bore of each of the detentmeans is a cross bore extending through the shaft, wherein the hub ofeach secondary weight has two diametrically opposite sockets opening toits bore, and wherein each detent means has two balls, one in each endportion of its cross bore.